WO 00 55089 A discloses a method and system for scrambling compressed or non-compressed digital samples representing audio and video data in such a manner that the content of these samples is degraded but recognizable or, if not, supplied with a required given quality. A given number of LSB's (least significant bits) of the data is scrambled for each sample frame by frame in an adaptive manner as a function of the dynamics of possible values and the most significant bits are unchanged. This solution represents an encrypting solution well known in the art with the aid of cryptographic keys. This method is not adaptive as a function of the content of the audiovisual stream nor as a function of other characteristics such as the throughput, type of frames, the user profile or the different layers of scalability characterizing it. Moreover, all the information initially contained in the stream remains inside the protected stream. This solution does not satisfy the criteria of strong security.
WO 01/97520, “Video Interface Device, Distribution System and Method of Transferring Programs and Encoded Video Sequences Through The Communication Network” discloses a device for the secure broadcasting of protected video streams. The protection of the video stream is brought about by replacing certain original images I by “false” images I or by interchanging certain images I among themselves. The original images I extracted from the video stream are stored separately from the protected stream and are sent to the user when he desires to view the video. Thus, replacing the original images I by “false” images I modifies the size of the protected stream relative to the original stream. Moreover, an ill-disposed user can readily detect a false image I with subscript n because this image with subscript n is very different from the image I with subscript n−1 and from image I with subscript n+1; the user can then easily replace it by image I with subscript n−1 or subscript n+1 or by an image calculated by interpolation between the images I with subscript n−1 and n+1, thus re-creating a stream very similar to the original one. Therefore, that solution does not satisfy the criterion of high security and adaptability of the protection of video streams.
EP 1 033 880 A2 (SHARP KK) discloses a process and device for protecting digital video streams and fixed images based on DCT and wavelet transformations. The modifications applied to the spatio-frequential coefficients are of the type: Scrambling of the bit of the sign of the coefficients, scrambling of the enhancement bits of the coefficients, scrambling of selected blocks and movement vectors in the P and B images, selection of appropriate coefficients belonging to a slice or to a frequential subband and interchanging them, bringing about the rotation of a block regrouping frequential coefficients. The protection is removed in a classic manner known to the expert in the art with the aid of decryption keys. EP '880 does not satisfy the security objectives because all the original data describing the stream is located inside the protective stream.
U.S. Pat. No. 5,754,658 (INTEL Corporation) discloses a method and a device for storing encoded data. The data is encrypted by different encryption techniques and the encryption is adaptive as a function of the overloading of the microprocessor of the encoder and/or of the decoder. The protection is not adaptive as a function of the desired visual degradation or as a function of the structure and the content of the video streams. Moreover, the applied protections are various encryption techniques and all the data initially presented remain integrally in the protected stream.
US 2001/0053222 A1 discloses a classic encryption solution based on keys. Even if the encryption is complex with four keys being used, all the information necessary for the reconstitution are present in the protected video stream.
WO 00/31964 (ERICSSON) relates to a method and equipment for the partial encryption of images and their progressive transmission. A first part of the image is compressed to a low quality without encryption and a second part (composed by two sections) of the image is encrypted. Each section is encrypted with its own method and its own key. This document presents a classic encryption step and therefore does not satisfy the criteria and objectives of our disclosure of high security because all the information describing the content is present inside the protected stream.
XP00997705 (Thomas KUNKELMANN and Uwe HORN) concerns the protection of video streams from video encoders based on DCT. In order to reduce the resources for the encryption, XP '705 proposes a method for a partial encryption of data based on the property of partitioning data while leaving the two parts physically in the same stream and based on scalabilities of time and space. XP '705 does not resolve the relevant problems because it proposes encryption techniques that are well-known in the art that interchange the data inside the stream or add encryption keys but while retaining all the data describing the stream inside it.
With the goal of separating a digital product into different portions in order to protect it, WO 01 69354 A3 (MICROSOFT CORP.) relates to the protection of a digital product (software or audio or video content) by breaking it down into at least two portions. The first portion is transmitted to the client equipment by physical means. The second portion is transformed in such a manner that it can only be used by the client station concerned, then it is transmitted integrally by the same process or by a communication network to this client station. The client station receiving the two portions can modify the first portion as a function of a key transmitted by the server from which key two other keys are generated in order that this first portion is compatible with the second portion received. These two portions are recombined together to restore a binary product modified in substance equivalent to the original product, but different in terms of configuration and adequate for the client equipment. WO '354 does not have any embodiment of a treatment performed on the two portions and no digital video format is cited. Moreover, the conformity with the original stream of either of the two parts initially separated is neither described nor suggested. Also, a separation of the digital product into two portions is made but all the elements of the digital product remain in the two portions transmitted to the user. The two encrypted portions are sent via two different paths and in two steps but are sent integrally. That invention does not satisfy the criteria of security and adaptation on the one hand on account of the use of the encryption method and on the other hand the adaptation limited to the equipment of each user.
It would therefore be advantageous to apply an adaptive and progressive scrambling as a function of the structure of the video bitstream and/or of its contents.